1. Field of the Invention
The present invention relates to moisture-curable resins containing alkoxysilane groups and optionally hydroxy groups, which can be cured in the presence of moisture to form coatings, adhesives and sealants, to a process for their production and to the compounds containing urea, isocyanate and alkoxysilane groups used to prepare the moisture-curable resins.
2. Description of the Prior Art
It is known that polyisocyanate resins are curable in the presence of atmospheric moisture to form polyurea coatings. During the curing mechanism an isocyanate group reacts with moisture to form an amino group, which then reacts with another isocyanate group to form a urea. One of the disadvantages of these moisture-curable resins is that the curing mechanism is relatively slow.
It has been suggested in U.S. Pat. Nos. 3,420,800 and 3,567,692 that the curing rate of moisture-curable polyisocyanates can be increased by incorporating either aldimines or ketimines. It is stated that the reaction of moisture with an aldimine or ketimine to form the corresponding amine is faster than the reaction of moisture with an isocyanate group to form an amine. A disadvantage of the use of aldimines and ketimines to accelerate the cure of polyisocyanates is that it requires the preparation of an additional component and requires some type of metering equipment to ensure that the two components are blended in the proper proportions.
Accordingly, there is a need to provide moisture-curable resins that do not require a co-reactant. Such resins have been disclosed in U.S. Pat. No. 5,364,955 and U.S. Pat. No. 5,766,751, which describe silane-terminated resins that have been prepared by reacting NCO prepolymers with silane aspartates to form either urea or hydantoin groups. The silane aspartates are prepared by initially reacting amino-functional silanes with maleic or fumaric acid esters. The silane aspartates are then reacted with NCO prepolymers to form the moisture-curable resins.
One of the disadvantages of this process is that it is not possible to prepare the silane-containing resins from higher functional polyols. When these polyols are reacted with polyisocyanates, primarily diisocyanates, gelation often occurs due to chain extension, even at NCO/OH equivalent ratios of 2:1.
U.S. Pat. No. 5,162,426 discloses the reaction of isocyanatoalkyl trialkoxysilanes with hydroxy-functional ethylenically unsaturated monomers and the subsequent polymerization of these unsaturated monomers with other unsaturated monomers to form silane-functional polymers. A disadvantage of these resins is the cost of the isocyanatoalkyl trialkoxysilanes.
Accordingly, it is an object of the present invention to provide silane-containing resins based on high functionality polyols, which do not suffer from the disadvantages of the prior art.
This object may be achieved with the moisture-curable resins according to the present invention and the process for their production, which are described in more detail hereinafter.